This invention generally relates to etching solutions and particularly to etching solutions for forming mask elements in silicon wafers.
The present technology of semiconductor devices requires high density device masks which necessitates the developing of line patterns in photoresist of less than one micron in width. Enclosure glass mask formation of such narrow lines is a problem due to the refraction of the light passing through the glass medium when developing the resist necessary to control the chrome erosion.
Electron beam proximity printing techniques which use silicon masks avoid these difficulties. Typical electron beam masks are described in U.S. Pat. Nos. 4,342,817 and 4,417,946, both of which are assigned to the present assignee. Masks shown in these patents have formed hole patterns in two micron thick membranes. Thus, light masking through the holes is not subject to refraction of the light passing through a medium other than that of air. In this way the photoresist, upon development has fewer irregularities than that encountered using the chrome glass mask medium.
In the referenced patents the silicon masks are created in a wet etching solution using an etching solution consisting of ethylene-diamine, pyrocatechol, water, and if necessary hydrogen peroxide solution. Specifically the solution consists of 72 grams of pyrocatechol, 630 mls. of ethylene-diamine, 115 mls. of water and 29 mls. of hydrogen peroxide. This solution, when used at temperatures of about 118.degree. C., is an anisotropic etchant of monocrystalline silicon with the 100 planes etched approximately 16 times quicker than the 111 planes.